1. Field of the Invention
The present invention relates to a Cu—Mg—P based copper alloy material suitable for electric and electronic components such as connectors, lead frames, relays, and switches, and more particularly, to a Cu—Mg—P based copper alloy material in which a tensile strength and a bending elastic limit value are balanced at a high level and a method of producing the same.
Priority is claimed on Japanese Patent Application No. 2009-291542, filed Dec. 23, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, electronic apparatuses such as mobile phones and laptop computers have been small, thin, and light, and smaller terminal and connector components, in which a pitch between electrodes is small, have been used. As a result of such miniaturization, the used material has become thinner. Due to the necessity for maintaining the connection reliability even though the material is thin, a material in which a bending elastic limit value and a higher strength are balanced at a high level is required.
Due to increases in the number of electrodes and an increase in electric current accompanying the increase in apparatus functionality, the generated Joule heat becomes large, and the need for a material with conductivity higher than that of prior cases becomes more pressing. Such a high conductive material is strongly required for a terminal and connector material for vehicles in which the increase in the electric current proceeds rapidly. Hitherto, brass or phosphor bronze has been generally used as such a terminal and connector material.
However, there is a problem that the generally and widely used brass and phosphor bronze cannot sufficiently answer the demand in regards to the connector material. That is, brass is lacking in strength, elasticity, and conductivity, and thus cannot cope with the miniaturization of the connector and the increase in the electric current. Phosphor bronze has higher strength and higher elasticity, but the conductivity thereof is low at about 20% IACS, and it is therefore difficult to cope with the increase in the electric current.
Phosphor bronze has a defect that its migration resistance is unsatisfactory. The migration means a phenomenon where Cu on the positive electrode side is ionized and precipitated into the negative electrode side when dew condensation or the like occurs between electrodes, to finally result in a short circuit between the electrodes. It causes a problem in connectors used in environments with high humidity such as vehicles, and it is a problem requiring care even in connectors in which a pitch between electrodes becomes narrow as a result of miniaturization.
As a material for solving the problems in such brass and phosphor bronze, for example, the applicant proposed a copper alloy using Cu—Mg—P as a main element as described in Japanese Patent Application Laid-Open No.H0 6-340938 (Patent Document 1) and Japanese Patent Application Laid-Open No.H09-157774 (Patent Document 2).
In Patent Document 1, a copper alloy material is disclosed which contains, by weight %, Mg of 0.1 to 1.0%, P of 0.001 to 0.02%, and the balance including Cu and inevitable impurities, in which surface crystal grains have an oval shape, an average short diameter of the oval shape crystal grains is 5 to 20 μm, a value of average long diameter/average short diameter is 1.5 to 6.0, an average crystal grains diameter in the final annealing just before the final cold rolling is adjusted within the range of 5 to 20 μm to form such oval shape crystal grains, and there is little abrasion of a stamping mold at the time of stamping in which a rolling rate in the final cold rolling process is within 30 to 85%.
In Patent Document 2, a thin copper alloy plate is disclosed which has a composition containing Mg of 0.3 to 2 weight %, P of 0.001 to 0.1 weight %, and the balance including Cu and inevitable impurities, in which a content of P is regulated in 0.001 to 0.02 weight %, a content of oxygen is adjusted in 0.0002 to 0.001 weight %, a content of C is adjusted in 0.0002 to 0.0013 weight %, and grain diameters of oxide grains including Mg dispersed in a basis material are adjusted to be 3 μm or smaller, and thus a decrease of a bending elastic limit value after a bending process is less than that of the known thin copper alloy plate. When a connector is produced from the thin copper alloy plate, the obtained connector has superior connector strength to those of the past and there is no case in which it deviates even when it is used under an environment of high temperature and vibration such as rotation of an engine of a vehicle.
It is possible to obtain a copper alloy having excellent strength, conductivity, and the like according to the inventions disclosed in Patent Document 1 and Patent Document 2. However, as electric and electronic apparatuses significantly increase in functionality, the performance of the copper alloy is required to be further improved. Particularly, in regards to the copper alloy used for the connectors and the like, it is important that deterioration does not occur in the use state and that it can be used however high the stress, and a Cu—Mg—P based copper alloy material in which a tensile strength and a bending elastic limit value are balanced at a high level is strongly required.
In the above-described Patent Document, the composition of the copper alloy and the shape of the surface crystal grains are regulated, but a relation between a tensile strength and a bending elastic limit value according to analysis of the fine structure of crystal grains was not described.